Exploring the occurrence of low cerebral oxygen in heart valve surgery and its impact on early prognosis.
190 patients who underwent elective heart valve surgery under mild hypothermia cardiopulmonary bypass (CPB) at West China Hospital of Sichuan University from August 2017 to May 2018 were included. Intraoperative monitoring of bilateral local brain tissue oxygen saturation (rSO2) in patients was conducted, and the occurrence of rSO2<55% for 5 minutes during surgery was defined as a low cerebral oxygen event. Patients were divided into a low cerebral oxygen group (L group) and a normal cerebral oxygen group (N group) based on whether low cerebral oxygen events occurred. Compare two sets of clinical data, analyze the occurrence of low cerebral oxygen and its impact on prognosis.
Among the included patients, 99 cases experienced low cerebral oxygen, and among the patients who experienced low cerebral oxygen, 73 cases occurred during CPB.
Half of the patients undergoing heart valve surgery experience low cerebral oxygen, which mostly occurs during CPB. Low cerebral oxygen can increase the incidence of AKI, blood lactate levels, and prolong the ICU stay and total hospital stay of patients.
Open heart surgery requires the assistance of extracorporeal circulation to ensure a clear, quiet, and bloodless surgical field while providing basic oxygen supply to the body, allowing the surgery to proceed safely and smoothly. However, during cardiopulmonary bypass (CPB), due to various reasons such as changes in hemodynamics, blood dilution, left shift of oxygen dissociation curve, and inflammatory response, the body is prone to imbalance between oxygen supply and consumption, resulting in oxygen debt and ultimately irreversible hypoxic damage and organ dysfunction. In the early stages of oxygen supply decline, traditional monitoring indicators show almost no abnormalities. However, when indicators reflecting oxygen supply and demand balance such as arterial oxygen saturation, mixed venous oxygen saturation, and blood lactate show abnormalities, local tissues often have been hypoxic for a period of time. Even if effective measures are taken immediately, the occurrence of hypoxic injury cannot be completely avoided, and in severe cases, it can lead to damage to important organ function or even death. In recent years, near-infrared spectroscopy (NIRS) technology has been applied to monitor the levels of oxygenated and non oxygenated hemoglobin in the frontal lobe cortex tissue of the brain, obtaining the oxygenation status of all blood in this area, including arterial blood, venous blood, and mixed arterial and venous blood,The local brain tissue oxygen saturation has the characteristics of non-invasive, real-time, and convenient. As a supplement to traditional monitoring methods, it has been applied in fields such as cardiovascular surgery, thoracic surgery, carotid endarterectomy, cardiopulmonary resuscitation, and neonatal intensive care.
This study mainly focuses on the occurrence of low brain tissue oxygen saturation (rSO2) in patients undergoing cardiac valve surgery assisted by CPB, analyzes its influencing factors and its relationship with patient prognosis, in order to provide a basis for better application of NIRS technology for perioperative management, and to provide ideas for maintaining oxygen supply and demand balance in perioperative management of cardiac surgery patients, avoiding oxygen debt, reducing the incidence of postoperative adverse events, and improving patient prognosis.
○1.1 General Information
Inclusion subjects: 190 patients who underwent elective heart valve surgery under mild hypothermia CPB at West China Hospital of Sichuan University from August 2017 to May 2018 were included, including 102 males and 88 females with an average age of (54.2 ± 11.97) years. The occurrence of bilateral local rSO2<55% for 5 minutes during surgery is defined as a low cerebral oxygen event in patients. According to whether a low cerebral oxygen event occurs, patients are divided into a low cerebral oxygen group (L group) and a normal cerebral oxygen group (N group).Inclusion criteria: (1) Age range of 18-80 years old;(2) Planned elective heart valve surgery; (3) The surgery requires CPB assistance.Exclusion criteria: (1) Suffering from central nervous system diseases;(2) History of central nervous system surgery; (3) The estimated surgical time is ≤ 2 hours.
○1.2 method
1.2.1 Preoperative baseline data collection:Collect baseline data of patients one day before surgery.1.2.2 Intraoperative monitoring:RSO2 monitoring: The brain tissue oxygen saturation monitor is used to monitor the rScO2 in both hemispheres of the patient's brain. Routine monitoring includes five lead electrocardiogram, pulse oxygen saturation, end expiratory carbon dioxide, invasive arterial pressure, central venous pressure, and nasopharyngeal temperature. Arterial blood samples were collected for blood gas analysis at the time of patient admission, before cardiopulmonary bypass surgery, every hour during cardiopulmonary bypass surgery, 20 minutes after cardiopulmonary bypass surgery, and when the surgeon closed the chest.1.2.3 Postoperative follow-up:Follow up indicators include: length of stay in the intensive care unit (ICU), total length of hospital stay; Hemoglobin, creatinine, urea nitrogen, AST/ALT values, brain natriuretic peptide (BNP), troponin; Postoperative complications (whether there are new cases of liver and kidney dysfunction).
○2.1 Occurrence of low cerebral oxygen eventsFinally, 190 patients undergoing heart valve surgery under superficial temperature CPB were included, of which 99 patients experienced low cerebral oxygen. Among the patients who experienced low cerebral oxygen, 73 patients occurred during CPB.○2.2 Baseline data comparisonThere were no statistically significant differences in gender, age, body mass index, ASA grading, preoperative hemoglobin, creatinine, urea nitrogen levels, AST/ALT values, troponin, left ventricular ejection fraction (EF) values, and left ventricular size between the two groups of patients (P>0.05). The preoperative blood glucose level in group L was lower than that in group N, and the BNP level was higher than that in group V (P<0.05), as shown in Table 1.
○2.3 Comparison of Follow up Results
There was no statistically significant difference (P>0.05) in the highest creatinine level, highest urea level, AST/ALT value, and postoperative EF value between group L and group N. The incidence of acute kidney injury (AKI), ICU stay time, total hospitalization time, highest postoperative BNP, and highest intraoperative lactate level in Group L were significantly higher than those in Group N (P<0.05), as shown in Table 2.
○2.4 Influencing factors of low cerebral oxygen eventsUsing binary logistic regression analysis, it was found that age>65 years and CPB time>120 minutes were risk factors for intraoperative low cerebral oxygen events (P<0.05), and rScO2>60% was a protective factor for low cerebral oxygen events, as shown in Table 3.
According to the standard of rSO2 absolute value less than 55% and lasting for more than 5 minutes as a low cerebral oxygen event, among the 190 patients included, 99 patients experienced low cerebral oxygen. Among the patients who experienced low cerebral oxygen, 73 cases occurred during CPB. ZHENG et al. systematically evaluated the use of brain NIRS monitoring in adult cardiac surgery patients and found that approximately 50% of cardiac surgery patients experienced one or more local decreases in rSO2 during the surgery, which is similar to the results of this study. The incidence of low cerebral oxygen in heart valve surgery is relatively high, mostly occurring during CPB. The rSO2 of patients decreases during CPB, mainly due to two reasons: the characteristics of oxygen supply and consumption during CPB, and the characteristics of energy utilization by brain tissue. During CPB, tissue perfusion pressure decreases, and non pulsatile blood flow replaces pulsatile blood flow, increasing the incidence of microcirculatory disorders. This non pulsatile blood flow also increases the release of catecholamines in the body, which can lead to local vascular constriction, reduced or no local tissue perfusion, and ultimately result in local tissue ischemia and hypoxia. CPB often has a certain degree of blood dilution, which not only increases the incidence of brain cell edema, but also reduces hemoglobin levels due to factors such as increased red blood cell damage caused by blood dilution, surgery, and CPB, as well as decreased deformability of red blood cells in the input stock blood. The effective oxygen carrying hemoglobin decreases, and tissues are prone to ischemia and hypoxia. Low perfusion leads to an increase in local tissue lactate production, a decrease in pH value, lower levels of diphosphoglycerate in stored blood, a decrease in arterial blood carbon dioxide concentration, and the need for hypothermia for myocardial protection, resulting in a leftward shift in the oxygen dissociation curve, oxygen dissociation disorders, and difficulty in tissue utilization of oxygen. In addition, when the concentration of carbon dioxide in arterial blood decreases, cerebral blood vessels contract, cerebral blood flow decreases, and brain tissue ischemia and hypoxia are prone to occur. At the beginning of CPB, due to the activation of immune cells such as monocytes and macrophages, contact between blood and CPB pipelines, changes in core body temperature, hemodynamic changes, and release of intestinal endotoxins, stress hormone levels significantly increase, and systemic inflammatory reactions are initiated. Excessive inflammatory reactions increase oxygen consumption in the body, making it more susceptible to ischemia and hypoxia.Due to the characteristics of cardiac surgery and CPB, about half of patients experience low cerebral oxygen during the surgery. The results of this study suggest that it is necessary to monitor cerebral oxygen in patients with CPB, especially during CPB, which can help detect brain tissue hypoxia in a timely manner.
Further analysis showed that there were statistically significant differences in ICU stay time, total hospital stay, postoperative AKI incidence, highest postoperative BNP, and highest intraoperative lactate between the low cerebral oxygen group and the normal cerebral oxygen group.The low cerebral oxygen group showed higher levels of lactate after CPB, highest postoperative BNP levels, and incidence of AKI, as well as longer ICU stay and total hospital stay.When low cerebral oxygen occurs, there is an imbalance between oxygen supply and demand in the local brain tissue, with oxygen demand exceeding oxygen supply. The aerobic oxidation process of glucose is hindered, and pyruvate cannot smoothly complete the tricarboxylic acid cycle production capacity. Acetoacetate is converted into lactic acid through anaerobic fermentation, causing hydrogen ion accumulation and a decrease in pH value inside the cell. At the same time, due to the decrease in adenosine triphosphate (ATP) produced by anaerobic fermentation, the energy supply to the cell is insufficient, leading to cell damage. Due to the above reasons, CPB causes tissue ischemia and hypoxia, leading to local lactate accumulation. After CPB, due to the restoration of pulsatile perfusion in tissues, the perfusion pressure increases, the peripheral circulation improves, and the accumulated lactate in local tissues is released into the blood, resulting in an increase in lactate content in the blood. In addition, after the restoration of normal circulation, the ischemia-reperfusion injury of various organs will further increase lactate levels. High lactate levels after CPB often indicate poor tissue perfusion, cellular ischemia and hypoxia, organ dysfunction, and an increased incidence of postoperative renal dysfunction. Lactic acid, as an indicator of poor tissue perfusion, is widely used in clinical practice. Hyperlipidemia is also a marker of circulatory failure, organ dysfunction, poor disease prognosis, and increased short - and long-term mortality. However, in clinical practice, the acquisition of lactate levels depends on blood gas tests, especially during CPB due to insufficient perfusion and other reasons. Lactic acid in the blood cannot fully reflect the tissue perfusion and oxygen supply and demand situation at this time, and has the characteristics of lag and inaccuracy. When the lactate level in the blood significantly increases, the tissue has been ischemic and hypoxic for a period of time, and even immediate remedial measures cannot completely avoid organ hypoxic damage.Compared to lactate, local rSO2 is a faster and more sensitive indicator for real-time monitoring of local tissue oxygen supply and demand.
This study also found that age>65 years and CPB duration>120 minutes are risk factors for the occurrence of low cerebral oxygen, while basal rSO2>60% is a protective factor for the occurrence of low cerebral oxygen events. Older patients are more likely to experience low cerebral oxygen, which is consistent with the results of multiple studies. As age increases, the body's functions gradually decline, brain cells shrink, brain volume decreases, cerebral oxygen metabolism slows down, cerebral blood vessels undergo degenerative changes, cerebral blood flow slows down, and under CPB conditions, it is more likely to produce an imbalance between oxygen supply and oxygen demand, leading to a decrease in local rSO2 and the occurrence of low cerebral oxygen events. Other studies have shown that as age increases, the distance of near-infrared light propagation in the skull increases, the propagation time increases, energy attenuation increases, and rSO2 decreases. Due to the characteristics of oxygen supply and consumption during CPB, as well as the utilization of energy by brain tissue, cerebral hypoxia damage is prone to occur during CPB. Long CPB time also means relatively high surgical difficulty and trauma, with increased destruction of red blood cells and blood dilution during the operation. As the surgical time prolongs, the probability of brain cell edema increases, the body's excessive inflammatory response, lactate accumulation, and left shift of the oxygen dissociation curve also increase the probability of low cerebral oxygen events occurring in the body.Reducing CPB time may decrease intraoperative cerebral oxygenationReduce the incidence of hypoxic brain injury.In summary, about half of patients undergoing heart valve surgery experience low cerebral oxygen, which mostly occurs during CPB. Low cerebral oxygen can increase the incidence of AKI, elevate blood lactate levels, prolong ICU stay and overall hospital stay for patients. Age>65 years and CPB duration>120 minutes are risk factors for intraoperative low cerebral oxygen, while baseline rSO2>60% is a protective factor. The Bolian Zhongke MOC series cerebral oxygen tissue saturation monitor can provide a targeted treatment method based on rSO2 dynamic monitoring. Through non-invasive, dynamic, and real-time monitoring methods, it provides clinical doctors with more accurate disease assessment and treatment adjustment basis, effectively improving the cerebral oxygen metabolism and inflammatory response of severe TBI patients, significantly improving the recovery speed and prognosis quality of patients.The Bolian Zhongke MOC series brain tissue oxygen saturation monitor can provide continuous, real-time, and non-invasive monitoring values of tissue oxygen saturation (rSO2), which can reflect specific organs (such as the brain, mesentery, kidneys, etc.) and systemic perfusion status. Research has shown that rSO2 monitoring can detect perfusion damage in the early stages that cannot be detected by conventional hemodynamic detection methods. It can timely monitor the oxygen supply and demand balance of brain and regional tissues, dynamic changes in cerebral blood flow, evaluate brain and tissue ischemia and hypoxia early, guide perioperative management, reduce the incidence of perioperative complications, sensitively reflect the oxygenation status of tissues and intervene, optimize the entire clinical treatment management, shorten hospitalization time, and improve patient prognosis.
